Optical disk device and optical disk discriminating method

ABSTRACT

An optical disk discriminating method and an optical disk device which can detect reflected rays for making discrimination among kinds of optical disks with high accuracies. By switching a plurality of lasers and moving a spherical aberration corrector while moving an objective lens to cause it to approach or keep away from an optical disk, rays reflected light from the optical disk can be detected with high accuracies. Discrimination among the kinds of a plurality of optical disks can be made on the basis of signals generated from the detected reflected rays. This ensures that the kind of an optical disk can be determined through one operation of sweeping.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese applicationJP2005-127309 filed on Apr. 26, 2005, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disk device and an opticalpickup and more particularly, to making discrimination among a pluralityof kinds of optical disks.

2. Description of the Related Art

In JP-A-8-287588, the thickness of a cover layer is decided todiscriminate the kind of an inserted optical disk by making the focus ofa light beam approach the optical disk and measuring a time for thefocus to reach an information recording layer from the surface of theoptical disk.

An available optical pickup capable of correcting spherical aberrationis constructed by having a beam expander disposed in an optical path offlux of light to add a predetermined spherical aberration, having aliquid crystal element for giving a predetermined spherical aberrationor having a means for changing the distance between two objective lensesin combination in the direction of focusing to provide sphericalaberrations. Presently, a technology has been known which uses anoptical pickup constructed as above to intentionally generate aspherical aberration in order to cancel out a spherical aberrationcaused by an error in cover thickness or an error in spacing betweeninformation recording layers.

SUMMARY OF THE INVENTION

With the increasing amount of data to be handled, the optical disk hasbeen acceleratedly increasing in its density and kinds. In order for anoptical disk device to respond to or comply with a plurality of kinds ofoptical disks, the optical disk device needs to discriminate the kind ofan inserted optical disk.

The thickness of a cover layer extending from the surface of an opticaldisk to an information recording layer, the corresponding laserwavelength and the track pitch differ with kinds of optical disks andtherefore, discrimination among the kinds is made on the basis offeatures of individual disks.

Recently, an increasing number of different kinds of semiconductorlasers are becoming available and, other than CD and DVD,standardization of Blu-ray Disc (hereinafter referred to as BD) andHD-DVD having ability to perform recording of higher density has atpresent been in progress.

In the BD, laser wavelength λ is shortened and NA (numerical aperture)of an objective lens of an optical pickup corresponding to or complyingwith the BD is widened and as a consequence, the aberration affectsgreatly. Especially, a spherical aberration SA is given by expression(1) where ΔT represents an error in thickness of the cover layer(hereinafter termed a cover thickness error) and λ represents awavelength of flux of light:

$\begin{matrix}{{SA} \propto \frac{\Delta\;{T \cdot {NA}^{4}}}{\lambda}} & (1)\end{matrix}$

Expression (1) indicates that the spherical aberration increases indirect proportion to a biquadrate of NA of the objective lens and errorΔT in thickness of the disk substrate and in inverse proportion to thelaser wavelength λ.

In JP-A-8-287588 as above, one laser is activated for illumination tomake discrimination. But, if a plurality of kinds of optical disks areirradiated using the one laser, desired characteristics of a reflectedray cannot be obtained in the presence of an optical disk unsuitable fora laser wavelength of the laser.

In addition, even if a laser beam suitable to an optical disk insertedin the optical disk device is irradiated, a light spot increases in sizeunless the spherical aberration is corrected properly, so that a desiredreflected ray cannot be obtained.

Specifically, in an optical disk constructed to have an informationrecording layer structure in the form of two or more layers, a sphericalaberration attributable to an error in spacing between the informationrecording layers takes place similarly to an error due to the coverthickness. Therefore, in the optical disk of multi-layer structure, thespherical aberration attributable to the error in the spacing betweenits recording layers must be corrected.

In the case of the optical disk of multi-layer structure, it isnecessary to detect how many information recording layers the focustransmits through but in case the irradiation is done with an unsuitedlaser wavelength or the spherical aberration is not corrected, theoptical disk can hardly be decided as to whether to be of a multi-layerstructure.

Further, even if a semiconductor laser for DVD or CD is activated foremission while making a spherical aberration corrector comply with a BD,a light spot cannot be focused successfully on the information recordingsurface of the DVD or CD. For this reason, the spherical aberrationcorrector must be adjusted in accordance with the kind of asemiconductor laser to be activated.

An object of the present invention is to detect reflected rays with highaccuracies to make discrimination among media irrespective of kinds ofoptical disks by sequentially illuminating a plurality of lasers ofdifferent wavelengths so as to change or switch the lasers forillumination and by making a suitable spherical aberration correction bymeans of the spherical aberration corrector, while moving an objectivelens for focusing a laser beam on the optical disk in the direction offocusing.

According to the present invention, even for an optical disk ofmulti-layer structure and optical disks causing different amounts ofspherical aberration, discrimination among the disks can be made withhigh accuracies.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an optical disk device according to afirst embodiment of the present invention.

FIG. 2 is a diagram showing connection from photodetectors to a signalprocessing circuit in the first embodiment of the invention.

FIG. 3 is a flowchart in the first embodiment of the invention.

FIGS. 4 to 8 are time charts showing signal waveforms in the firstembodiment of the invention.

FIG. 9 is a block diagram showing an optical disk device according to asecond embodiment of the present invention.

FIG. 10 is a flowchart in the second embodiment of the invention.

FIG. 11 is a time chart showing signal waveforms in the secondembodiment of the invention.

FIG. 12 is a block diagram showing an optical disk device according to athird embodiment of the present invention.

FIG. 13 is a flowchart in the third embodiment of the invention.

FIGS. 14 and 15 are time charts showing signal waveforms in the thirdembodiment of the invention.

FIG. 16 is a block diagram showing an optical disk device according to afourth embodiment of the present invention.

FIG. 17 is a flowchart in the fourth embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of this invention will now be described with reference tothe accompanying drawings. An optical disk device of the invention canbe of any type including a device dedicated to reproduction, a devicededicated to recording or a recording/reproduction device, on conditionthat it can make discrimination among optical disks. As far as thepresent invention is concerned, the reproduction only device andrecording only device differ from each other in that either reproductionor recording is carried out after discrimination among optical disks hasbeen made. On the other hand, the recording/reproduction device canperform recording or reproduction after discrimination among opticaldisks.

Referring first to FIG. 1, an optical disk device and optical pickupaccording to the present invention is constructed as illustrated thereinin block form.

An optical disk 100 rotatable by means of a spindle motor 101 undergoesinformation read, erase or write under irradiation of a laser beam.

A semiconductor laser 102 emits a laser beam for BD. Flux of light ofthe laser beam is passed through a beam splitter 105, reflected by amirror 107, shaped into parallel light flux by means of a collimate lens108, reflected by a dichroic mirror 110, passed through a quarter-waveplate 112, passed through a spherical aberration corrector 113,reflected by a mirror 114 and caused by an objective lens 115 to beformed into a light spot 116 on an information recording layer ofoptical disk 100. A reflected ray from the optical disk 100 travels aroute similar to the going route so as to be reflected by the beamsplitter 105, passed through a cylindrical lens 117 and detected by aphotodetector 119.

A semiconductor laser 103 emits a laser beam for DVD. Flux of light ofthe laser beam is passed through a dichroic mirror 111, passed through abeam splitter 106, shaped into parallel light flux by means of acollimate lens 109, passed through the dichroic mirror 110, passedthrough the quarter-wave plate 112, passed through the sphericalaberration corrector 113, reflected by the mirror 114 and formed by theobjective lens 115 into a light spot 116 on the information recordinglayer of optical disk 100. A reflected ray from the optical disk 100travels a route similar to the going route so as to be reflected by thebeam splitter 106, passed through a cylindrical lens 118 and detected bya photodetector 120.

A semiconductor laser 104 emits a laser beam for CD. Flux of light ofthe laser beam is reflected by the dichroic mirror 111, passed throughthe beam splitter 106, shaped into parallel light flux by the collimatelens 109, passed through the dichroic mirror 110, passed through thequarter-wave plate 112, shaped into a divergent beam by means of thespherical aberration corrector 113, reflected by the mirror 114 andformed by the objective lens 115 into a light spot 116 on theinformation recording layer of optical disk 100. A reflected ray fromthe optical disk 100 travels a route similar to the going route so as tobe reflected by the beam splitter 106, passed through the cylindricallens 118 and detected by the photodetector 120.

The spherical aberration corrector 113 is an optical element forcorrecting a spherical aberration attributable to an error in thethickness of cover layer and is comprised of, for example, a so-calledbeam expander in which two lenses of variable inter-lens distance areused in combination and the inter-lens distance is changed and adjustedby a drive signal from a spherical aberration corrector drive circuit202 so that the spherical aberration of passing light flux may becorrected. The spherical aberration corrector is not limited to thistype but for example, it may be a liquid crystal element which has aconcentric pattern to provide a phase difference between inner and outercircumferential portions of flux of light, thereby attaining the aboveeffect. In any case, the corrector is adapted to correct sphericalaberrations in compliance with the respective laser beams from theplurality of semiconductor lasers. It is now assumed that the sphericalaberration corrector is conditioned to exhibit status SAb suitable forBD, status SAd suitable for DVD and status SAc suitable for CD. Valuessuited to the status are set pursuant to, for example, standards of BD,DVD and CD and stored in advance in a memory of the optical disk device.Products of optical disk device are uneven and therefore the values maypreferably be set differently product by product.

The objective lens 15 is a triple-wave correspondent lens which iscontrolled by an actuator 121 in tracking direction and focusingdirection so as to be changed in its NA in accordance with a laserwavelength for BD, a laser wavelength for DVD and a laser wavelength forCD. As the objective lens, a multi-focus objective lens is used whichchanges in focal point in accordance with laser beams of a plurality ofwavelengths.

The dichroic mirror is an element for reflecting or transmitting laserbeams in accordance with differences in laser wavelength and especially,the dichroic mirror 110 is an element for reflecting the laserwavelength for BD and transmitting the laser wavelengths for DVD and CDand the dichonic mirror 111 is an element for transmitting the laserwavelength for DVD and reflecting the laser wavelength for CD.

The photodetector 119 outputs a signal corresponding to a reflected rayof the laser beam for BD from the optical disk and the output signalconnects to an input terminal (a) of a change-over switch 150.

The photodetector 120 outputs signals corresponding to reflected rays ofthe laser beams for DVD and CD from the disk and the output signalsconnect to an input terminal (b) of the change-over switch 150.

A spindle motor drive circuit 200 is a circuit controlled by a systemcontroller 300 to drive the spindle motor 101, an actuator drive circuit201 is a circuit controlled by the system controller 300 to drive theactuator 121, the spherical aberration corrector drive circuit 202 is acircuit controlled by the system controller 300 to drive the sphericalaberration corrector 113, and a laser drive circuit 203 is a circuitcontrolled by the system controller 300 to activate the semiconductorlasers 102 to 104 for emission.

The change-over switch 150 responds to a transfer signal SEL deliveredout of the system controller 300 to selectively output the input signalsand its output signals connect to a signal processing circuit 204.

Turning to FIG. 2, the photodetector 119, photodetector 120, change-overswitch 150 and signal processing circuit 204 are connected to oneanother as illustrated therein. The photodetector (four-elementphotodetector) 119 is comprised of quarter photo-detectors A1, B1, C1and D1. Likewise, the photodetector (four-element photodetector) 120 iscomprised of quarter photo-detectors A2, B2, C2 and D2. Outputs of thequarter photo-detectors A1 and A2 are connected to a transfer switch 151and outputs of the quarter photo-detectors B1 and B2 are connected to atransfer switch 152. Outputs of the quarter photo-detectors C1 and C2are connected to a transfer switch 153 and outputs of the quarterphoto-detectors D1 and D2 are connected to a transfer switch 154.

In the transfer switches 151 to 154, the photo-detectors A1, B1, C1 andD1 are connected to provide signals A, B, C and D, respectively, whenthe transfer signal SEL is 1 and photo-detectors A2, B2, C2 and D2 areconnected to provide signals A, B, C and D, respectively, when thetransfer signal SEL is 2. In other words, the change-over switch 150responds to the SEL signal to perform switching between the output ofthe photodetector 119 for detection of reflected light from a BD and theoutput of the photodetector 120 for detection of reflected light from aDVD or CD, thus selectively supplying the outputs to the signalprocessing circuit 204. As described above, the number of output signalsfrom each of the photodetectors 119 and 120 is four and the number ofoutput signals from the change-over switch is also four but in FIG. 1,for simplification of illustration, the respective output signals areput together and indicated by one. The system controller 300 outputs theSEL signal such that the photodetector 119 can be connected to thesignal processing circuit 204 when the semiconductor laser 102 isactivated but it outputs the SEL signal such that the photodetector 120can be connected to the signal processing circuit 204 when thesemiconductor laser 103 or 104 is activated.

In FIG. 2, the signal processing circuit 204 includes adders andsubtracters. Here, all of the signals A, B, C and D are added togetherto provide (A+B+C+D) which is a sum signal PE of reflection signals fromthe optical disk 100 (hereinafter referred to as PE signal). Also,(A+C)−(B+D) provides a focus error signal based on the known astigmatismmethod (hereinafter referred to as FE signal).

By using the PE signal and FE signal, the system controller 300discriminates the kind of the optical disk 100 pursuant to a method tobe described later.

Illustrated in FIG. 3 is a flowchart of a discriminating method in thepresent embodiment. In step 1-1, discrimination is started. In step 1-2,sweeping is started. “Sweeping” referred to herein signifies that theactuator drive circuit 201 responds to a signal from the systemcontroller 300 to move the actuator 121 so that the objective lens 115may be moved in the direction of focusing. Assumptivley, in thefollowing description, sweeping for causing the objective lens 115 toapproach the optical disk 100 is called up-sweep and conversely, todepart or keep away from the optical disk 100 is called down-sweep. Instep 1-2, down-sweep is first carried out to separate the objective lens115 from the optical disk 100 to a remote movable end and thereafterup-sweep is executed.

In step 103, the semiconductor laser 102 for BD is turned on to emit alaser beam for BD. In step 1-4, the spherical aberration corrector 113is moved so as to be brought into the status SAb. In step 1-5, it isdecided whether the disk is a BD or not. If YES in the step 1-5, theprogram proceeds to step 1-6 in which the optical disk 100 is determinedas a BD. If No in the step 1-5, the program proceeds to step 1-7 inwhich the semiconductor laser 102 for BD is turned off.

In step 1-8, the semiconductor laser 103 for DVD is turned on to emit alaser beam for DVD. In step 1-9, the spherical aberration corrector 113is moved so as to be brought into the SAd status. In step 1-10, it isdecided whether the disk is a DVD. If YES in the step 1-10, the programproceeds to step 1-11 in which the optical disk 100 is determined as aDVD. If No in the step 1-10, the program proceeds to step 1-12 in whichthe semiconductor laser 103 for DVD is turned off.

In step 1-13, the semiconductor laser 104 is turned on to emit a laserbeam for CD. In step 1-14, the spherical aberration corrector 113 ismoved so as be brought into the SAc status. In step 1-15, it is decidedwhether the disk is a CD. If YES in the step 1-15, the program proceedsto step 1-16 in which the optical disk 100 is determined as a CD. If Noin the step 1-15, the program proceeds to step 1-17 in which the opticaldisk is determined as an optical disk the optical disk device cannotcomply with or no insertion of optical disk into the optical disk deviceis determined and in step 1-18, the semiconductor laser 104 for CD isturned off. In step 1-19, the status of spherical aberration corrector113 is returned to the initial status.

The step 1-6, 1-11, 1-16 or 1-19 is followed by step 1-20 in whichsweeping is ended and the discrimination process ends in step 1-21.

After completion of the discrimination process, the laser and thespherical aberration corrector are placed in condition suitable for theoptical disk 100 and therefore, focus pull-in can be done with highaccuracy.

A detailed description will be given of the flowchart of FIG. 3hereunder. A method for discriminating the disk as to whether to be aBD, a method for discriminating the disk as to whether to be a DVD and amethod for discriminating the disk as to whether to be a CD will bedetailed with reference to FIGS. 4 and 5, FIGS. 6 and 7 and FIG. 8,respectively.

Referring to FIG. 4, there is illustrated a time chart useful to explaina discriminating method when the optical disk 100 is a BD of one layer.While sweeping has already been started, the semiconductor laser 102 forBD is activated to emit a laser beam (laser 102 in FIG. 4 is in Hicondition) and the spherical aberration corrector is in the SAb status.FE and PE signals are used to decide whether the focus of the laser beamreaches the surface of optical disk 100. When the voltage level of FEsignal crosses Vhp and Vhm and the voltage level of PE signal crossesVh, reaching the surface is determined. As the voltage level of PEsignal falls below Vh, time is measured. Then, if, after the lapse ofapproximate time Tbs (for example, an error of ±10%), the FE signalsequentially crosses Vbp and Vbm and the voltage level of PE signalcrosses Vb1 for a time of about Tb1, the optical disk 100 is determinedas a mono-layer BD.

Turning to FIG. 5, there is illustrated a time chart useful to explain adiscriminating method when the optical disk 100 is a double-layer BD.Reaching the surface is determined in a similar way to FIG. 4 and timeis measured at the time that the voltage level of PE signal falls belowVh. Then, if after the lapse of approximate time Tbd, the voltage levelof FE signal crosses twice Vbp during rise and Vbm during fallreiteratively and besides the voltage level of PE signal crosses Vb2 fora time of about Tb2, the optical disk 100 is determined as adouble-layer BD.

Turning to FIG. 6, there is illustrated a time chart useful to explain adiscriminating method when the optical disk 100 is a mono-layer DVD. Incase the discrimination condition for BD is not satisfied by the FE andPE signals within time Tb after arrival at the surface is determined asin the case of FIG. 4, the optical disk 100 is determined as not being aBD and the semiconductor laser 102 for BD is turned off (laser 102 inFIG. 6 is in Low condition) and the semiconductor laser 103 for DVD isactivated for emission (laser 103 in FIG. 6 is in Hi condition).Further, the status of spherical aberration corrector is shifted fromSAb to SAd suited for DVD. Then, if, at the termination of a time ofabout Tds after the voltage level of PE signal has fallen below Vh, theFE signal sequentially crosses Vdp and Vdm and besides the voltage levelof PE signal crosses Vd1 for a time of about Td1, the optical disk 100is determined as a mono-layer DVD.

Turning to FIG. 7, there is illustrated a time chart for explaining adiscriminating method when the optical disk 100 is a double-layer DVD.As in the case of FIG. 6, the semiconductor laser 102 for BD is turnedoff, the semiconductor laser 103 for DVD is activated and the status ofspherical aberration corrector is shifted from SAb to SAd suited forDVD. Time is measured as the voltage level of PE signal falls below Vh.Then, if, at the termination of a time of about Tdd, the voltage levelof FE signal crosses twice Vdp during rise and Vdm during fallreiteratively and besides the voltage level of PE signal crosses Vd2 fora time of about Td2, the optical disk 100 is determined as adouble-layer DVD.

Turning to FIG. 8, there is illustrated a time chart for explaining adiscriminating method when the optical disk 100 is a mono-layer CD. Asin the case of FIG. 6, reaching the surface is determined, the opticaldisk 100 is determined as not being a BD, the semiconductor laser 102for BD is turned off and the semiconductor laser 103 for DVD isactivated. Thereafter, if the discrimination condition for DVD is notsatisfied by the FE and PE signals within a time of Td, the optical disk100 is determined as not being a DVD, so that the semiconductor laser103 for DVD is turned off (laser 103 in FIG. 8 in Low condition) and thesemiconductor laser 104 for CD is activated (laser 104 in FIG. 8 is inHi condition). Further, the status of spherical aberration corrector isshifted from SAd to SAc suited for CD. If, at the termination of a timeof about Tcs after the voltage level of PE signal has fallen below Vh,the FE signal sequentially crosses Vcp and Vcm and besides the voltagelevel of PE signal crosses Vc for a time of about Tc1, the optical disk100 is determined as a CD. Contrarily, if the discrimination conditionfor CD is not satisfied by the FE and PE signals during a time Tcfollowing activation of the semiconductor laser 104 for CD, it isdetermined that no disk is inserted in the optical disk device and thesemiconductor laser 104 for CD is turned off.

Now, the speed of sweeping will be described. In connection with FIGS. 6and 7, the sum of time Tsd required for moving the spherical aberrationcorrector from the status SAb to the status SAd suitable for DVD andtime Tb needs to be far smaller than time Tds or time Tdd and inconnection with FIG. 8, the total of time Tsc required for moving thespherical aberration corrector from the status SAd to the status SAcsuited for CD, time Tb and time Td needs to be far smaller than timeTcs. The above conditions can be expressed by conditional expression(2):Tds>Tsd+TbTdd>Tsd+TbTcs>Tsc+Tb+Td  (2)

It is now assumed that the sweeping speed is constant amounting to Vsw,a cover layer extending from the surface of a BD to its informationrecording film is Db in thickness, a cover layer extending from thesurface of a DVD to its information recording layer is Dd in thicknessand a cover layer extending form the surface of a CD to its informationrecording layer is Dc in thickness. Then, conditions expressed byexpression (3) must be satisfied between the Vsw and the Tb, Td and Tc.

$\begin{matrix}{{{Tb} > \frac{Db}{Vsw}}{{{Tb} + {Td}} > \frac{Dd}{Vsw}}{{{Tb} + {Td} + {Tc}} > \frac{Dc}{Vsw}}} & (3)\end{matrix}$

A sweeping speed Vsw satisfying the above six conditional formulas isset and then the Tb, Td and Tc are set on the basis of the set sweepingspeed. In addition, the sensitivity of the actuator is uneven and thethickness of the cover layer is also uneven and therefore, theunevenness is also taken into consideration for setting.

As described as above, in embodiment 1 of the invention, activation ofthe semiconductor lasers is switched with time in order of BD, DVD andCD to make discrimination among the media. Conditions for discriminationrepresented by time, voltage level and time for switching lasers arestored in advance in a memory medium such as a memory of the opticaldisk device. In the present embodiment, execution of switchingsemiconductor lasers and discrimination among media are referenced tothe lapse of time following detection of the surface but in the case ofan optical pickup having an objective lens whose position in thedirection of focusing can be measured, a method may also be employedaccording to which the laser switching and the determination among mediaare carried out without depending on the lapse of time but on the basisof a distance over which the objective lens moves in the focusingdirection after completion of detection of the surface. It will beappreciated that in the present method, the distance between the surfaceof optical disk 100 and the objective lens 115 at the time that thefocus of the laser beam is irradiated on the information recording layerof optical disk 100 must differ depending on the kind of the opticaldisk.

The above-described method is applicable to the case where the opticalpickup has such a characteristic that the position of objective lens115, taken up when the laser beam is focused on the informationrecording layer of optical disk 100, approaches the optical disk 100 inorder of BD, DVD and CD. If the optical pickup has such a characteristicthat the position of objective lens 115, taken up when the laser beam isfocused on the information recording layer of optical disk 100,approaches the optical disk 100 in order of BD, CD and DVD, thesemiconductor lasers for BD, CD and DVD are activated in this orderfollowing start of up-sweep and the spherical aberration corrector isalso moved in order of the status suited for BD, status suited for CDand status suited for DVD. This can ensure that the kind of optical disk100 can be determined through one sweeping operation.

Embodiment 2

Referring now to FIG. 9, a second embodiment of the present inventionwill be described. Components in FIG. 9 designated by the same referencenumerals as those in FIG. 1 are identical to the constituents explainedin connection with embodiment 1.

An optical disk device of FIG. 9 does not comprise the objective lens115 correspondent to three wavelengths of BD, DVD and CD in FIG. 1 butis comprised of an objective lens 122 for focusing a laser beam for BDand an objective lens 123 correspondent to two wavelengths of DVD andCD. A laser beam for BD is focused by means of the objective lens 122for BD and laser beams for DVD and CD are focused by means of theobjective lens 123 for DVD/CD. The objective lens 122 is moved by anactuator 124 and the objective lend 123 is moved by an actuator 125.

A dichroic mirror 126 reflects a laser beam for BD so as to lead thelaser beam for BD to the objective lens 122 but transmits the laserbeams for DVD and CD. The laser beams for DVD and CD having transmittedthrough the dichroic mirror 126 are reflected by the mirror 114 so as tobe led to the objective lens 123.

Illustrated in FIG. 10 is a flowchart of a discriminating method in thepresent embodiment. In step 2-1, optical disk discrimination is started.In step 2-2, the semiconductor laser 102 for BD is activated. In step2-3, the status of spherical aberration corrector 113 is shifted to SAbsuited for BD. In step 204, the objective lens 122 is kept away from theoptical disk 100 to a remote movable end and thereafter, it undergoesup-sweep. In step 2-5, it is decided whether the disk is a BD. Thediscrimination conditions used herein are identical to those in themethod described in embodiment 1 with reference to FIGS. 4 and 5 inwhich the surface and the recording surface are detected in accordancewith signal levels and discrimination is made on the basis of timerequired for sweeping from the surface to the recoding surface, with theexception that laser switching is not executed with time and theobjective lens 122 is swept up to a movable end close to the opticaldisk 100. If YES in the step 2-5, the program proceeds to step 2-6 inwhich the disk is determined as a BD. If No in the step 2-5, the programproceeds to step 2-7 in which the disk is determined as not being a BDand the BD laser is turned off.

In step 2-8, the semiconductor laser 103 for DVD is activated. In step2-9, the status of spherical aberration corrector 113 is brought intoSAd suited for DVD. In step 2-10, it is decided whether the disk is aDVD. Discrimination conditions used herein are identical to those usedin the method explained in embodiment 1 with reference to FIGS. 6 and 7in which the surface and the recording surface are detected inaccordance with signal levels and discrimination is made on the basis oftime required for sweeping from the surface to the recording surface,with the exception that laser switching is not executed with time andthe objective lens 123 is swept up to a movable end close to the opticaldisk 100. If YES in the step 2-10, the program proceeds to step 2-11 inwhich the disk is determined as a DVD. If No in the step 2-10, theprogram proceeds to step 2-12 in which the disk is determined as notbeing a DVD and the laser for DVD is turned off.

In step 2-13, the optical disk 100 is presumptively determined as a CD.In step 2-14, the semiconductor laser 104 for CD is activated. In step2-15, the status of spherical aberration corrector 113 is brought intoSAc suited for CD. In step 2-16, the objective lens 123 is separatedfrom the optical disk 100 to a remote movable end and subsequentlyup-sweep is carried out to start focus pull-in. In step 2-17, it isdecided whether a focus servo can be turned on. If YES in the step 2-17,the program proceeds to step 2-18 in which the disk is determined as aCD. If No in the step 2-17, the program proceeds to step 2-19 in whichthe disk is determined as not being a correspondent disk and in step2-20, the laser for CD is turned off.

After completion of the step 2-6, 2-12, 2-18 or step 2-20, sweeping isended in step 2-21 and the process for making discrimination amongoptical disks is ended in step 2-22.

Turning to FIG. 11, a discriminating method when the optical disk 100 isa CD will be described. An indication “objective lens moving status” inFIG. 11 signifies that as the objective lens 123 moves from low to high,it approaches the optical disk 100. If, after arrival at the surface,the optical disk 100 is determined as neither BD nor DVD, the disk isassumed to be a CD as in the case of FIG. 10. Thereafter, thesemiconductor laser 104 for CD is activated, the objective lens isseparated from the optical disk 100 to a remote movable end and thestatus of spherical aberration corrector is set to SAc suited for CD.Then, focus pull-in is started through up-sweep. If the focus servosystem can be turned on after completion of the focus pull-in, the diskis determined as a CD.

In the method of the present embodiment, the medium discrimination timein the case of the optical disk 100 being a CD can be shortened ascompared to embodiment 1.

Embodiment 3

Next, a third embodiment of the present invention will be described withreference to FIG. 12. Components in FIG. 12 designated by the samereference numerals as those in FIGS. 1 and 9 are identical to theconstituents explained in embodiments 1 and 2. Objective lenses 122 and123 are moved by means of an actuator 121.

Like embodiment 1, a laser beam for BD is shaped into parallel flux oflight by the collimate lens 108 and then passed through the quarter-waveplate 112 and spherical aberration corrector 113 and reflected by themirror 114 so as to be led to the objective lens 122. As in the case ofembodiment 1, laser beams for DVD and CD are each shaped into parallelflux of light by a collimate lens 109 and then, passed through aquarter-wave plate 126, reflected by a mirror 127 and led to theobjective lens 123. Accordingly, in the present invention, only thelaser beam for BD is passed through the spherical aberration corrector113.

A flowchart of a discriminating method according to the presentembodiment is depicted in FIG. 13. Assumptively, prior to start ofdiscrimination, the status of spherical aberration corrector 113 on theoptical path has already been set to SAb. In step 3-1, discrimination isstarted. In step 3-2, up-sweep of the objective lenses 122 and 123 iscarried out after they have been separated from the optical disk 110 toremote movable ends.

In step 3-3, the semiconductor laser 102 is turned on to emit a laserbeam for BD. In step 3-4, it is decided whether the surface can bedetected. If No in the step 3-4, the program proceeds to step 3-5 inwhich no insertion of optical disk into the optical disk device isdetermined and in step 3-6, the laser for BD is turned off. If YES inthe step 3-4, the program proceeds to step 3-7 in which the disk isdecided as to whether to be a BD. If YES in the step 3-7, the programproceeds to step 3-8 in which the optical disk 100 is determined as aBD. If No in the step 3-7, the program proceeds to step 3-9 in which thesemiconductor laser 102 for BD is turned off.

In step 3-10, the semiconductor laser 103 for DVD is turned on to emit alaser beam for DVD. In step 3-11, the disk is decided as to whether tobe a DVD. If YES in the step 3-11, the program proceeds to step 3-12 inwhich the optical disk 100 is determined as a DVD. If No in the step3-11, the program proceeds to step 3-13 in which the laser for DVD isturned off.

In step 3-14, the semiconductor laser 104 for CD is turned on. In step3-15, the disk is decided as to whether to be a CD. If YES in the step3-15, the program proceeds to step 3-16 in which the disk is determinedas a CD. If No in the step 3-15, the program proceeds to step 3-17 inwhich the optical disk 100 is determined as an optical disk the opticaldisk device does not corresponds to or no insertion of optical disk intothe optical disk device is determined and in step 3-18, the laser for CDis turned off.

After completion of the step 3-6, 3-8, 3-12, 3-16 or 3-18, sweeping isended in step 3-19 and the process for making discrimination amongoptical disks is ended in step 3-20.

Discrimination conditions for BD, DVD and CD are the same as those inthe method explained in embodiment 1 with reference to FIGS. 4 to 8. Amethod for determination of CD in the present embodiment is depicted inFIG. 14. Firstly, the semiconductor laser 102 for BD is turned on andthe surface is detected. If the discrimination condition for BD is notsatisfied within time Tb, the semiconductor laser 102 for BD is turnedoff and instead, the semiconductor laser 103 for DVD is turned on. Atthat time, since a laser beam for DVD does not pass through thespherical aberration corrector, no spherical aberration correction ismade for the beam. If, with the semiconductor laser 103 for DVD turnedon, the discrimination condition for DVD is not satisfied within timeTd, the semiconductor laser 103 for DVD is turned off and instead thesemiconductor laser 104 for CD is turned on. Since a laser beam for CDdoes not pass through the spherical aberration corrector, either, nospherical aberration correction is made for the beam. If, with thesemiconductor laser 104 for CD turned on, the discrimination conditionfor CD is satisfied within time Tc, the disk is determined as a CD butif not satisfied, the optical disk 100 is determined as an optical diskthe optical disk device does not corresponds to or no insertion ofoptical disk is determined.

Referring to FIG. 15, there is illustrated a time chart for explaining amethod for deciding the surface. In case the voltage level of PE signalcrosses Vh for a time of about Thh within time Th following activationof the laser for BD, the surface is so determined as to be passed by. Ifthis condition is not satisfied, no insertion of optical disk into theoptical disk device is determined. Alternatively, the time Th may not beset but the objective lens 122 may be swept throughout the overallmovable range to determine whether the aforementioned decision conditionis satisfied.

As in the case of embodiment 1, it is also necessary in the method ofthe present embodiment that the distance between the optical disk 100and each of the objective lenses 122 and 123 at the time that the focusof the laser beam is irradiated on the information recording layer ofoptical disk 100 differ with the kind of the optical disk.

Embodiment 4

Turning now to FIG. 16, a fourth embodiment of the invention will bedescribed. Components in FIG. 16 designated by the same referencenumerals as those in FIGS. 1, 9 and 12 are identical to the constituentsexplained in embodiment 1 with reference to FIGS. 1 to 3.

An optical disk device in FIG. 16 comprises an objective lens 128corresponding to two wavelengths for BD and DVD and an objective lens129 correspondent to CD. The objective lenses 128 and 129 are switchedsuch that one of them is set on an optical path and when thesemiconductor laser 102 for BD and semiconductor laser 103 for DVD areactivated, the objective lens 128 for BD and DVD is on the optical pathand when the semiconductor laser 104 for CD is activated, the objectivelens 129 for CD is on the optical path. Like embodiment 1, the objectivelenses 128 and 129 are moved by means of the actuator 121.

A dichroic mirror 130 is an element for reflecting a wavelength of laserbeam for BD but transmitting a wavelength of laser beam for DVD and adichroic mirror 131 is an element for transmitting wavelengths of laserbeams for BD and DVD but reflecting a wavelength of laser beam for CD.

A photodetector 132 outputs signals corresponding to reflected rays oflaser beams for BD and DVD from the optical disk and the output signalsare connected to the input terminal (b) of change-over switch 150.

A photodetector 133 outputs a signal corresponding to a reflected ray ofa laser beam for CD from the disk and the output signal is connected tothe input terminal (a) of change-over switch 150.

The change-over switch 150 responds to an SEL signal to performswitching between the outputs of the photodetector 132 for detection ofreflected rays for BD and DVD and the output of the photodetector 133for detection of a reflected ray for CD and supply a selected output tothe signal processing circuit 204. The SEL signal is a transfer signalfor connecting the input terminal (b) to the signal processing circuit204 when the semiconductor laser 102 for BD or the semiconductor laser103 for DVD is turned on and for connecting the input terminal (a) tothe signal processing circuit 204 when the semiconductor laser 104 forCD is turned on.

A flowchart of a discriminating method of the present embodiment isdepicted in FIG. 17. Assumptively, before starting discrimination, theobjective lens 128 for BD and DVD is set on the optical path. In step4-1, discrimination is started. In step 4-2, the objective lens 128 isseparated from the optical disk 100 to a remote movable end andthereafter, up-sweep is conducted.

In step 4-3, the semiconductor laser 102 is turned on to emit a laserbeam for BD. In step 4-4, the spherical aberration corrector 113 ismoved to bring its status into SAb. In step 4-5, it is decided whetherthe disk is a BD. If YES in the step 4-5, the program proceeds to step4-6 in which the optical disk 100 is determined as a BD. If No in thestep 4-5, the program proceeds to step 4-7 in which the semiconductorlaser 102 for BD is turned off.

In step 4-8, the semiconductor laser 103 for DVD is turned on to emit alaser beam for DVD. In step 4-9, the spherical aberration corrector 113is moved to bring its status into SAd. In step 4-10, it is decidedwhether the disk is a DVD. If YES in the step 4-10, the program proceedsto step 4-11 in which the optical disk 100 is determined as a DVD. If Noin the step 4-10, the program proceeds to step 4-12 in which the laserfor DVD is turned off.

In step 4-13, the objective lens on the optical path is switched fromthe objective lens 128 for BD and DVD to the objective lens 129 for CD.In step 4-14, the semiconductor laser 104 for CD is turned on. In step4-15, it is decided whether the disk is a CD. If YES in the step 4-15,the program proceeds to step 4-16 in which the disk is determined as aCD. If No in the step 4-15, the program proceeds to step 4-17 in whichthe optical disk 100 is determined as an optical disk the optical diskdevice does not corresponds to or no insertion of optical disk into theoptical disk device is determined and in step 4-18, the laser for CD isturned off.

Following the step 4-6, 4-11, 4-16 or 4-18, sweeping is ended in step4-19 and the process for making discrimination among optical disks isended in step 4-20.

Discrimination conditions for BD, DVD and CD are the same as those inthe method explained in embodiment 1 with reference to FIGS. 4 to 8.But, while in FIG. 8 the status of the spherical aberration correctorfor CD is set to SAc, this correction is not made in the presentembodiment.

Like embodiment 1, the distance between the optical disk 100 and each ofthe objective lenses 128 and 129 at the time that the focus of the laserbeam is irradiated on the information recording layer of optical disk100 must differ with the kind of optical disk also in the presentembodiment.

Differing from embodiment 3, the present embodiment allows the sphericalaberration correction to be made even for DVD. The DVD is a double-layerdisk which is susceptible to spherical aberration and for this reason,with the spherical aberration corrected, more accurate signals can bedetected. Further, if the spherical aberration correction is desired tobe made also for DVD in embodiment 3, the optical pickup may beconstructed such that the laser beam for DVD can pass through thespherical aberration corrector.

In embodiments 1 to 4, the kind of optical disk 100 can be determinedthrough one sweeping operation. In addition, the kind of optical disksthe optical disk device can deal with amounts up to three kinds of BD,DVD and CD but even in an optical disk device correspondent to anotherkind of disk, for example, HD-DVD, discrimination can be accomplishedthrough a similar method.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. An optical disk device comprising: an optical pickup including aplurality of semiconductor lasers having different wavelengths, anobjective lens, an actuator for moving said objective lens to cause itto approach or keep away from a recording surface of an optical disk, aspherical aberration corrector for correcting spherical aberrations oflaser beams and photodetectors for detecting reflected rays from saidoptical disk; a drive circuit for actuating said semiconductor lasersand drive circuits for moving said actuator and said sphericalaberration corrector, respectively; a signal processing circuit forgenerating signals from the reflected rays detected by saidphotodetectors; and a system controller for outputting a control signalto said drive circuit adapted to move said actuator so as to move aidobjective lens in relation to said optical disk, outputting controlssignals for activating said plurality of lasers of different wavelengthsto said drive circuit and a control signal for controlling saidspherical aberration corrector to said drive circuit and discriminatingthe kind of said optical disk from signals generated from said signalprocessing circuit, said spherical aberration corrector being operativeto correct spherical aberrations in correspondence with respective onesof said plurality of semiconductor lasers.
 2. An optical disk deviceaccording to claim 1, wherein focus pull-in is effected under the statusof said spherical aberration corrector set when the kind of an opticaldisk inserted in said optical disk device is determined.
 3. An opticaldisk discriminating method for making discrimination among a pluralityof kinds of optical disks in an optical disk device having an opticalpickup including a plurality of semiconductor lasers of differentwavelengths, an objective lens, an actuator for moving said objectivelens to cause it to approach or keep away from a recording surface of anoptical disk and photodetectors for detecting reflected rays from saidoptical disk, said method comprising the steps of: irradiating laserbeams of different wavelengths on said optical disk by switching saidplurality of lasers in order while moving said objective lens to causeit to approach or keep away from the recording surface of said opticaldisk; detecting reflected rays from said optical disk under irradiationof the laser beams; generating signals of the detected reflected rays;and determining from said signals which one of said plurality of kindsof optical disks said optical disk belongs to.
 4. An optical diskdiscriminating method according to claim 3, wherein at the time thatpassage of the focus of a laser beam through the surface of said opticaldisk is detected while moving said objective lens to cause it toapproach the recording surface of said optical disk, measurement of timeis started and laser beams are irradiated on said optical disk byswitching said plurality of lasers of different wavelengths in order inaccordance with measured times or moving distances of said objectivelens; rays reflected from said optical disk under irradiation of thelaser beams are detected; and it is decided, on the basis of signalsgenerated from the detected reflected rays, which one of said pluralityof kinds of optical disks said optical disk belongs to.
 5. An opticaldisk discriminating method according to claim 4, wherein whendetermination of the surface of an optical disk is conducted in vain, noinsertion of optical disk into said optical disk device is determined.6. An optical disk discriminating method according to claim 3, whereinsaid signal includes a focus error signal or a signal indicative of thesum of reflected rays, or both and the kind of said optical disk isdiscriminated by measuring levels of changes in said signal and times.7. An optical disk discriminating method according to claim 3, whereintimes for timing of switching lasers are stored in advance in saidoptical disk device.
 8. An optical disk discriminating method accordingto claim 3, wherein if making discrimination among optical disks isconducted in vain even when all kinds of lasers are illuminated inorder, no insertion of optical disk into said optical disk device orinsertion of an optical disk said optical disk device does notcorrespond to is determined.
 9. An optical disk discriminating methodaccording to claim 3, wherein at the time that the kind of an opticaldisk inserted in said optical disk device is determined, switching thelasers is stopped.
 10. An optical disk discriminating method for makingdiscrimination among a plurality of kinds of optical disks in an opticaldisk device having an optical pickup including a plurality ofsemiconductor lasers of different wavelengths, an objective lens, anactuator for moving said objective lens to cause it to approach or keepaway from a recording surface of an optical disk, a spherical aberrationcorrector for correcting spherical aberrations, and photodetectors fordetecting reflected rays from said optical disk, said method comprising:irradiating laser beams on said optical disk by switching said pluralityof lasers of different wavelengths in order while moving said objectivelens to cause it to approach or keep away from the recording surface ofsaid optical disk; concurrently with switching the lasers forillumination, correcting spherical aberrations of the respective laserbeams emitted from said plurality of lasers in correspondence with therespective switched lasers by means of said spherical aberrationcorrector; detecting rays reflected from said optical disk underirradiation of the laser beams; generating signals from the detectedreflected rays; and deciding which one of said plurality of kinds ofoptical disks said optical disk belongs to.
 11. An optical diskdiscriminating method according to claim 10, wherein at the time thatpassage of the focus of a laser beam through the surface of said opticaldisk is detected while moving said objective lens to cause it toapproach the recording surface of said optical disk, measurement of timeis started and laser beams are irradiated on said optical disk byswitching said plurality of lasers of different wavelengths in order inaccordance with measured times or moving distances of said objectivelens; concurrently with switching the lasers for illumination, sphericalaberrations of the respective laser beams emitted from said plurality oflasers are corrected in correspondence with the respective switchedlasers by means of said spherical aberration corrector; rays reflectedfrom said optical disk are detected under irradiation of the laserbeams; and it is decided which one of said plurality of kinds of opticaldisks said optical disk belongs to.
 12. An optical disk discriminatingmethod according to claim 11, wherein at the time that passage of thefocus of a laser beam through the surface of said optical disk isdetected while moving said objective lens to cause it to approach therecording surface of said optical disk, measurement of time is startedand laser beams are irradiated on said optical disk by switching saidplurality of lasers of different wavelengths in order in accordance withmeasured times or moving distances of said objective lens; concurrentlywith switching the lasers for illumination, spherical aberrations of therespective laser beams emitted from said plurality of lasers arecorrected in correspondence with the respective switched lasers by meansof said spherical aberration corrector; and if discrimination cannot bemade even when irradiation operations are conducted by the number whichis one smaller than the number of kinds of the lasers, it is determinedthat said optical disk is a medium suited for the remaining one laserand switching to the one laser is effected so that spherical aberrationmay be so corrected as to meet said one laser and the focus pull-in maybe effected.
 13. An optical disk discriminating method according toclaim 12, wherein when the focus pull-in is started with the laserlastly activated for illumination but in vain, the optical disk insertedin said optical disk device is determined as being of the kind of anoptical disk said optical disk device does not correspond to.
 14. Anoptical disk discriminating method according to claim 12, wherein whendetermination of the surface of an optical disk is conducted in vain, noinsertion of optical disk into said optical disk device is determined.15. An optical disk discriminating method according to claim 11, whereinwhen determination of the surface of an optical disk is conducted invain, no insertion of optical disk into said optical disk device isdetermined.
 16. An optical disk discriminating method according to claim10, wherein said signal includes a focus error signal or a signalindicative of the sum of reflected rays, or both and the kind of saidoptical disk is discriminated by measuring levels of changes in saidsignal and times.
 17. An optical disk discriminating method according toclaim 10, wherein times for timing of switching lasers and the status ofthe spherical aberration corrector to be shifted simultaneously withswitching lasers are stored in advance in said optical disk device. 18.An optical disk discriminating method according to claim 10, wherein ifmaking discrimination among optical disks is conducted in vain even whenall kinds of lasers are illuminated in order, no insertion of opticaldisk into said optical disk device or insertion of an optical disk saidoptical disk device does not correspond to is determined.
 19. An opticaldisk discriminating method according to claim 10, wherein when noinsertion of optical disk into said optical disk device or insertion ofan optical disk said optical disk device does not correspond to isdetermined, said spherical aberration corrector is returned to theinitial status.
 20. An optical disk discriminating method according toclaim 10, wherein at the time that the kind of an optical disk insertedin said optical disk device is determined, switching the lasers isstopped.
 21. An optical disk discriminating method according to claim10, wherein in correcting spherical aberrations of the respective laserbeams emitted from said plurality of semiconductor lasers, respectively,in correspondence with the respective lasers simultaneously withswitching the lasers for illumination by means of said sphericalaberration corrector, said spherical aberration corrector is adjusted tosuch a degree that discrimination conditions for making discriminationamong kinds of optical disks can be detected from signals generated fromrays reflected from said optical disks.